A new study from the University of Waterloo found that snakes optimize their vision when they perceive a threat by controlling the blood flow to their eyes. Snakes have a clear spectacle over their eyes that acts as sort of a window and protects the eyes. The researchers serendipitously found, while studying a different part of a snake’s eyes, that these spectacles have a network of bloods vessels that are sort of like the blinds in the window. They found a constriction in the presence of threatening stimuli. In perceived danger, the vessels kept the blood flow reduced for longer periods, up to several minutes at a time, to guarantee the best possible visual capacity in times of greatest need.